In general, microwave and millimeter-wave (MMW) communication systems are constructed with various components and subcomponents such as receiver, transmitter, and transceiver modules, as well as other passive and active components, which are fabricated using MIC (Microwave Integrated Circuit) and/or MMIC (Monolithic Microwave Integrated Circuit) technologies. The system components/subcomponents can be interconnected using various types of transmission media such as printed transmission lines (e.g., microstrip, slotline, CPW (coplanar waveguide), CPS (coplanar stripline), ACPS (asymmetric coplanar stripline), etc.) or coaxial cables and waveguides.
Printed transmission lines are widely used in microwave and MMW circuits to provide package-level or circuit board-level interconnects between semiconductor chips (RF integrated circuits) and between semiconductor chips and transmitter or receiver antennas. Moreover, printed transmission lines are well suited for signal propagation on the surface of a semiconductor integrated circuit. For instance, CPW transmission lines are widely used in MMIC designs due to their uniplanar nature, low dispersion and high compatibility with active and passive devices. However, printed transmission lines may be subject to parasitic modes and increased losses at high frequencies. On the other hand, metallic waveguides (e.g., rectangular, circular, etc.) are suitable for signal transmission over larger distances and at high power levels in a low-loss manner. Furthermore, waveguides may be shaped into a highly directive antennas or may be used for device characterization.
When constructing microwave, RF or MMW systems, it may be necessary to couple a printed transmission line with a waveguide using a coupling structure referred to a “transition”. Transitions are essential for integrating various components and subcomponents into a complete system. The most common transmission line-to-waveguide transitions are microstrip-to-waveguide transitions, which have been widely studied. While considerable research and development has been dedicated to such transitions, comparatively less effort has been applied to establish suitable transitions from CPW, CPS or ACPS transmission lines to rectangular waveguides. CPW and CPS transmission lines are particularly suitable (over microstrip) for high integration density MIC and MMIC designs. In this regard, it is highly desirable to develop broadband, low-loss and well matched transitions between waveguides and CPW or CPS printed transmission lines or monolithic microwave integrated circuits (MMICs) which can be used to design high performance systems.